A photocatalyst layer is formed on a surface of a construction material, glass, or the like, and irradiated with ultraviolet light or visible light. Then, the photocatalyst is excited to decompose or remove an organic substance or demonstrate hydrophilicity, anti-fogging properties, dirt resistance, and the like. When the surface of a construction material, glass, or the like is hydrophilic, a contact angle made with water becomes smaller, and water droplets adhering to the surface spread to form a water film. Thereby, fading of the surface coating by the water droplets can be prevented, or fogging caused by adhesion of fine water droplets can be prevented which improves visibility. Even if dirt adheres to the surface of a construction material, glass, or the like, the hydrophilic effect of the photocatalyst allows water such as rain water to invade under the dirt and remove the dirt. Thereby, the dirt is easily washed off, and a dirt resistance effect is provided. Further, various applications are found, for example, a water film is formed on wall surfaces by the photocatalytic hydrophilicity in summer, thereby the wall is cooled and the room temperature is controlled.
Conventionally, in fixing the construction material, glass, or the like, a sealant is used in a connected portion (joint portion) of the construction materials or a gap between glass and a frame (a sash portion) mainly in order to prevent invasion of rain water or absorb expansion or shrinkage of the construction materials, glass, and the like caused by an external stress. Examples of the sealant include mainly four sealants such as silicone sealants, modified silicone sealants, polysulfide sealants, and polyurethane sealants. A photocatalyst layer is contaminated by bleeding of a plasticized component contained in all of these sealants and becomes water repellant condition and difficult to demonstrate the photocatalytic hydrophilic effect. For this reason, according to the description of Patent Literature 1, in order to prevent elution of a plasticized component contained in a sealant, a fluorine resin coating film, a silicone resin coating film, a modified silicone resin coating film, a polysulfide resin coating film, or a polyisobutylene resin coating film is formed on the surface of the sealant.